1. Field of the Invention
This invention relates to a method of fabricating an on-demand ink jet print head, and more particularly to a method of fabricating an ink jet print head in which a low-rigidity member having a rigidity lower than that of a piezoelectric member constitutes a part of a side wall of a pressure chamber.
2. Description of the Related Art
Conventional ink jet print heads are disclosed in Japanese Patent Laid Open No. Hei 5-64893 and Japanese Patent Laid Open No. Hei 5-96727. The structure of the ink jet print head will be described hereinafter in a fabricating process order, following which the operation thereof will be described.
First, as shown in FIG. 6 (A), a predetermined gap is produced between a base plate 1 such as a glass plate and a piezoelectric member 2 which is polarized along the thickness thereof, and adhesive is used to fill up the space between the base plate 1 and the piezoelectric member 2. After that the adhesive is cured to form an adhesive layer 3 between the base plate 1 and the piezoelectric member 2.
Next, as shown in FIG. 6 (B), a plurality of grooves 4 are cut in the surface of the piezoelectric member 2 so that the grooves 4 extend into the adhesive layer 3 and side walls 5 are formed on both sides of the grooves 4. Then, electrodes 6 are formed on an inner surface of the grooves 4.
Further, as shown in FIG. 6 (C), a top plate 7 is stuck to the surface of the piezoelectric member 2. The top plate 7 includes an ink supplying groove 9 (see FIG. 7) formed therein. Through this process, the upper openings of the grooves 4 are closed by the top plate 7, so that the side walls 5 and top plate 7 define a plurality of pressure chambers 8.
After that, as shown in FIG. 7, an orifice plate 11 is stuck to the sides of the base plate 1, adhesive layer 3 and piezoelectric member 2. An orifice plate 11 is provided with a plurality of orifices 10 each of which serves as an ink jet nozzle. Thus, the ink jet print head is completed.
Next, the operation of the ink jet print head thus constructed will be described hereinafter. FIG. 8 is a cross sectional view showing a part of the ink jet print head. In FIG. 8, a central pressure chamber is designated by reference numeral 8b, a left side pressure chamber by reference numeral 8a, and a right side pressure chamber by reference numeral 8c. An example of the operation of jetting the ink from the central pressure chamber 8b will be described.
Electric fields are generated on the side wall 5 between the central pressure chamber 8b and the left pressure chamber 8a and the side wall 5 between the central pressure chamber 8b and the right pressure chamber 8c, in opposite directions. Then, the walls 5 are deformed such that the volume of the central pressure chamber 8b is increased. This reduces the internal pressure of the central pressure chamber 8b to suck ink from the ink supplying groove 9. In this case, though the right and left pressure chambers 8a, 8c are compressed, the right and left pressure chambers are prevented from jetting ink because the voltage applied to the electrodes 6 is gradually increased to apply the electric field so as to gradually decrease the volume of the right and left pressure chambers 8a, 8c. In this stage, the electrodes 6 are grounded immediately, then the volume of the central pressure chamber 8b is rapidly decreased, so that the internal pressure of the central pressure chamber 8b is rapidly increased. Thus, the central pressure chamber 8b jets ink through the orifice 10.
In this case, each side wall 5 defining the pressure chamber 8 is made of the piezoelectric member 2 and the adhesive layer 3 having a rigidity lower than that of the piezoelectric member 2, so that resistance against strain of the piezoelectric member 8 is reduced, thus it is possible to increase the amount of strain of the piezoelectric member 2. Thus, the jetting characteristics are improved.
Next, problems of this conventional art will be described hereinafter. When fabricating the ink jet print head, it is necessary to form the adhesive layer 3 in a predetermined thickness over an entire surface. However, since it is difficult to get a uniform curing and contraction action of the adhesive over a wide surface, a thickness t.sub.1 of the adhesive layer 3 varies, so that, as shown in FIG. 9(A), the center of the piezoelectric member 2 is warped to be pulled by the adhesive layer 3. Even if the upper surface of the piezoelectric member 2 is evenly ground as shown with a dotted line 12, and after that the top plate 7 is stuck to the piezoelectric member 2 as shown in FIG. 9(B), a thickness t.sub.2 of the piezoelectric member 2 of the side wall 5 defining the pressure chamber 8 and a thickness t.sub.3 of the adhesive layer 3 of the side wall 5 may vary in places. Therefore, the displacement characteristics of the each side wall 5 become unequal when applying voltage to the electrodes 6, so that it is impossible that pressure chambers 8 uniformly jet ink.